PtBi/C Electrocatalysts for Formic Acid Electro-Oxidation in Acid and Alkaline Electrolyte

Pt/C and PtBi/C with different PtBi atomic ratio (90:10, 80:20, 70:30, 60:40 and 50:50) were prepared by borohydride reduction method using H2PtCl6·6H2O and Bi(NO3)3·5H2O as metal sources and Vulcan XC72 as carbon support. The electrocatalysts prepared were characterized by X-ray diffraction, transmission electron microscopy and cyclic voltammetry. The activity for the formic acid electro-oxidation in acid and alkaline electrolyte was investigated at room temperature by cyclic voltammetry and chronoamperometry. X ray diffraction showed for all PtBi/C the presence of Pt face-centered cubic (fcc) system, while for PtBi/C (70:30, 60:40 and 50:50) electrocatalyst it was also observed the presence of some peaks that could be attributed to the presence of Bi metallic, Bi oxide species or PtBi phases. TEM micrographs and histograms for PtBi/C electrocatalysts showed that the nanoparticles are well dispersed on the support with particle sizes of 2.5±1.5 nm for all electrocatalysts prepared, however some agglomerates were also observed. The electrochemical studies showed that PtBi/C (90:10) had superior performance for formic acid electro-oxidation at 25oC in presence of acidic electrolyte compared to Pt/C, this result indicated that the addition of Bi to Pt could favor the electro-oxidation of formic acid and this effect could be attributed to the bifunctional mechanism associated to electronic effect. However in the alkaline electrolyte it was observed that Pt/C electrocatalysts had superior performance in comparison with PtBi/C, this result indicated that an optimization of the formic acid concentration for alkaline studies is still necessary.